Welding Design 1. This topics will be discuss discussed ed in one session of the lecture 2. However, an extensive discussion about welding will NOT be covered for mechanical program such as: Stresses in welded joint in torsion and bending The strength of welded joints Static and fatigue loading applied on welded joints Resistance welding
Permanent Permanent
Joints
joint covers joint such as:
Welding
Brazing Soldering Cementing Gluing The advantages of permanent joint are it will eliminate fasteners, holes, and assembly cost
Welding Symbols
Basic
Weld Symbols
Fillet
Welds
Butt
and
Fillet
Welds
A
Transverse
Fillet
Weld
This stress can be divided into two components, a shear stress and a normal stress. There are
In fig. below these are entered into a Morr¶s circle diagram. The largest principal stress is seen to be
Stress Distribution in Welds
Fillet
Thus the equation for average stress is
and is normally used in designing joints having fillet welds.
A
double-filleted lap joint double-
Since there are two welds, the throat area for both is
The average shear stress is therefore
(9--3) (9
Torsion in Welded Joints The reaction at the support cantilever always consists of a shear force V and a moment M. The shear force produces a primary shear in the welds of magnitude (9--4) (9 W here A
is the throat area of all the welds. The moment at the support produces secondary shear or torsion of the welds, and this stress is (9--5) (9 r = distance from the centroid
J = polar moment inertia
Figure
9-11 A moment connection 9-
Figure
9--12 shows two welds in a group. The rectangle represent the throat areas of 9 the welds. W eld 1 has a throat width b1 ± 0.70hl; and weld 2 has a throat width d2 = 0.707h2. Note that h1 and h2 are the respective weld sizes. The throat area of both welds is A
= A1 + A2 = B1D1 + B2D2
(a)
Since the throat width of a fillet weld is 0.707h, the relationship between the unit polar moment of inertia and the polar moment of inertia of a fillet weld is J = 0.707hJu
Table 99-1 Torsional Properties of Fillet W elds
EXAMPLE
9-1 9-
50 kN load is transferred from a welded fitting into a 200mm steel as illustrated in figure 99-13. Compute the maximum stress in the weld.
A
Solution a) Label the end and corners of each weld by letter. Sometimes it is desirable to label each weld of a set by number. See figure 99-14 b) Compute the primary shear stress. As shown in figure 99-13 each plate is welded to the channel using three 6mm fillet welds. Figure 99-14 show that we have divided the load in half and are considering only a single plate. From case 4 of table 9 9--1 we find the throat area as A
